Dynamic studies of the initial events of photoreception and transduction in the primary visual process are proposed. Kinetic spectroscopy enables us to investigate the sequential intermediates which are initiated by the absorption of a photon by the molecular photoreceptor rhodopsin. Experiments are designed to elucidate the nature of the conformational intermediates, their potential energy surfaces, and their kinetic transformations. The link between these intermediate events, and the next step in triggering a change in the membrane potential of the photoreceptor cell, is sought. The mechanism of activation of photoreceptor cGMP phosphodiesterase by rhodopsin is being examined to determine whether the activation is part of the cellular triggering and/or a response modulating cellular sensitivity.